Monatin is a high-intensity sweetener having the chemical formula:

Because of various naming conventions, monatin is also known by a number of alternative chemical names, including: 2-hydroxy-2-(indol-3-ylmethyl)-4-aminoglutaric acid; 4-amino-2-hydroxy-2-(1H-indol-3-ylmethyl)-pentanedioic acid; 4-hydroxy-4-(3-indolylmethyl)glutamic acid; and 3-(1-amino-1,3-dicarboxy-3-hydroxy-but-4-yl)indole.
Monatin contains two chiral centers leading to four potential stereoisomeric configurations. The R,R configuration (the “R,R stereoisomer” or “(R,R)-monatin”); the S,S configuration (the “S,S stereoisomer” or “(S,S)-monatin”); the R,S configuration (the “R,S stereoisomer” or “(R,S)-monatin”); and the S,R configuration (the “S,R stereoisomer” or “(S,R)-monatin”). The different stereoisomers of monatin have different sweetening characteristics.
Certain isomeric forms of monatin can be found in the bark of roots of the Schlerochiton ilicifolius plant located predominately in the Limpopo region, but also in Mpumalanga and the North West Province of South Africa. However, the concentration of the monatin present in the dried bark, expressed as the indole in its acid form, has been found to be about 0.007% by mass. See U.S. Pat. No. 4,975,298. The exact method by which monatin is produced in the plant is presently unknown.
At least in part because of its sweetening characteristic, it is desirable to have an economic source of monatin. Furthermore, because of the different sweetening characteristics of the different stereoisomers, it is desirable to have an economic source of a single stereoisomer of monatin, such as the R,R stereoisomer. Thus, there is a continuing need to develop methods for the production of monatin in stereoisomerically-pure or stereoisomerically-enriched form.